TATB is an insensitive energetic material used in various military applications. TATB is used in warhead fuzes and also as the explosive component in insensitive high explosives, such as in plastic bonded explosive compositions. TATB has been produced from various starting materials, such as 1,3,5-trichlorobenzene, 3,5-dichloroanisole, 3,5-dibromoanisole, trinitrobenzene, picramide, or phloroglucinol. While various methods of producing TATB are known, TATB is no longer available from a qualified supplier for Department of Defense applications.
U.S. Pat. No. 4,032,377 to Benziger describes synthesizing TATB from 1,3,5-trichlorobenzene. The 1,3,5-trichlorobenzene is nitrated, producing 1,3,5-trichloro-2,4,6-trinitrobenzene (“TCTNB”), which is then aminated to produce TATB. In addition to TATB, ammonium chloride is produced as an impurity. The nitration and amination reactions are conducted at a temperature of 150° C. for an extended period of time. The pressure during the amination reaction is from 35 psig to 40 psig. The TATB produced by this process is referred to herein as so-called “legacy TATB.” This process is currently qualified by the U.S. Department of Energy and the U.S. Department of Defense. However, the 1,3,5-trichlorobenzene starting material is toxic, and environmentally hazardous waste streams are produced in its manufacture, making it an ever increasingly less attractive material. As such, the production of 1,3,5-trichlorobenzene is currently conducted only outside of the United States, such as in China. With no domestic sources of 1,3,5-trichlorobenzene available, production of legacy TATB within the United States is an expensive prospect with an uncertain and unreliable source of starting material.
One method of synthesizing TATB from phloroglucinol is described in GB 2355715. Phloroglucinol, also known as 1,3,5-trihydroxybenzene, is nitrated using sodium nitrite and nitric acid, forming trinitrophloroglucinol (“TNPG”), which is also known as 1,3,5-trihydroxy-2,4,6-trinitrobenzene. The nitric acid is added sequentially or in multiple additions. When cooled, a solid is produced, which is filtered, washed with 3 M hydrochloric acid (“HCl”), and dried, yielding a solid product that is a monohydrate of TNPG. The monohydrate of TNPG is a free-flowing solid. The TNPG is alkoxylated using a trialkyl orthoformate, such as trimethyl orthoformate, forming 1,3,5-trimethoxy-2,4,6-trinitrobenzene. Methanol and methyl formate are also formed and are removed by distillation. The solution of 1,3,5-trimethoxy-2,4,6-trinitrobenzene is concentrated, yielding 1,3,5-trimethoxy-2,4,6-trinitrobenzene as a solid, which is recrystallized from ethanol. The purified 1,3,5-trimethoxy-2,4,6-trinitrobenzene is then aminated using liquid ammonia or gaseous ammonia, filtered, washed with N-methylpyrrolidinone and methanol, and dried, yielding crystals of the TATB. To conduct the amination reaction, a solution of the 1,3,5-trimethoxy-2,4,6-trinitrobenzene is cooled to −10° C. and ammonia gas is introduced. If liquid ammonia is used, the animation reaction is conducted at room temperature and a pressure of 8-9 bar, or at atmospheric pressure and −33° C. If gaseous ammonia is used, the animation reaction is conducted at atmospheric pressure or at a pressure of 8-9 bar. At higher temperatures, the method is described as being less energy efficient. The TATB synthesis utilizes multiple drying and isolation acts to produce solid products of TNPG, TETNB, and TATB.
Another method of synthesizing TATB from phloroglucinol is described in co-pending U.S. patent application Ser. No. 11/744,986 to Velarde et al., entitled “METHODS OF PRODUCING 1,3,5-TRIAMINO-2,4,6-TRINITROBENZENE.” For convenience, this process is referred to herein as the “Velarde process” and the above-mentioned patent application is referred to herein as the “Velarde application.” The TATB produced by this process is referred to herein as so-called “Velarde TATB.” In the Velarde process, the phloroglucinol is nitrated to produce TNPG, which is then alkoxylated to produce a 1,3,5-trialkoxy-2,4,6-trinitrobenzene, such as 1,3,5-triethoxy-2,4,6-trinitrobenzene (“TETNB”). The 1,3,5-trialkoxy-2,4,6-trinitrobenzene is then aminated, producing TATB. TATB produced by this process possesses an amorphous, agglomerate crystal structure, has a purity of 98%-99% (as measured by high pressure liquid chromatography (“HPLC”)), and has lower thermal stability (as measured by DSC onset) than legacy TATB. The amorphous, agglomerate structure of the TATB results in a low bulk density. Impurities produced during the process include ammonium diaminopicrate (“ADAP”) salt and ethoxydiaminotrinitrobenzene (“EDATB”). The agglomerates of TATB are greater than approximately 50 μm in diameter and are formed from agglomerates of smaller-sized TATB, which decreases the sensitivity of the TATB.
One major difficulty associated with the synthesis of TATB results from its insolubility in most organic solvents, even at an elevated temperature. TATB is sparingly soluble in dimethyl sulfoxide (“DMSO”) (i.e., 0.047% solution in DMSO at 21° C.), dimethylformamide (“DMF”), acetonitrile, and concentrated sulfuric acid. Due to this insolubility, TATB having the crystal structure or crystal morphology ultimately desired in the final product must be obtained as the result of the synthesis. If the incorrect crystal structure is obtained, recrystallization of the TATB to obtain the correct crystal morphology is not practical.
It would be desirable to synthesize TATB from an environmentally friendly starting material. The TATB produced may exhibit comparable purity, thermal stability, and crystal morphology as legacy TATB, and improved purity, thermal stability, and crystal morphology compared to TATB produced by other known processes.